The judgment below is reversed, and the case is remanded to Busan High Court.

The grounds of appeal are examined (to the extent of supplement in case of supplemental appellate briefs not timely filed).

1. The principle of trust and good faith (hereinafter “new rule”) refers to an abstract norm that, in consideration of the other party’s interest, a party to a legal relationship should not exercise a right or perform a duty in a way that is contrary to equity or trust.

In order to deny the exercise of rights on the ground that it violates the good faith principle, it should be given to the other party with good faith or objectively deemed that the other party has good faith. The exercise of rights against the other party’s good faith should have to reach such a level that is unreasonable in light of the concept of justice.

If the contents of the labor-management agreement, such as a collective agreement, are null and void in violation of the Labor Standards Act’s compulsory provisions, and the assertion of invalidation is rejected on the ground that it is an exercise of rights contrary to the good faith principle, the legislative intent of which is stipulated as the compulsory provisions will be reversed, and such assertion is not in violation of the

However, since the contents of the labor-management agreement violate the compulsory provisions of the Labor Standards Act, it does not exclude the application of the good faith principle without exception to the allegation that the labor-management agreement is invalid.

It is not only a general requirement for applying the above principle of good faith, but also an exceptional case where there are extenuating circumstances that agree to preferentially apply the principle of good faith despite the compulsory nature of the Labor Standards Act, claiming the invalidity of the labor-management agreement is not permissible in violation of the principle of good faith.

Under the premise that regular bonuses do not themselves constitute ordinary wages in the labor-management agreement, it is to exclude regular bonuses from the calculation standard of ordinary wages.